The title of this game is a bit of a lie. It implies it’s one of those cookie clicker type idler games where you kill things, but actually, there’s a lot of non-idle “gameplay” needed in order to actually progress.
The basic idea is you run left to right, automatically, and collect coins and kill baddies. Coins let you buy upgrades for your equipment which basically act as coins-per-second increases and multipliers, meaning more coins more quickly with which to buy more stuff to repeat the cycle with ever-increasing numbers going up.

So, it’s same as most of games like this. However, there’s a second currency – souls – which can only be earned by resetting all your progress. You collect them mainly from slaying foes, but can’t actually use them until you wipe out all your upgrades, coins and equipment and start again. The souls can then be spent on permanent upgrades and unlockables. This too I’ve seen in other games and is sometimes called “prestiging”. Later, there’s also a third type of currency which you can sort of “super prestige” with, which also wipes out your permanent upgrades but lets you buy other properly permanent upgrades. Oh, and there’s a gem currency which you can buy various thing with but requires Real Actual Money, so I never touched it.
The “idle” bit which isn’t though, is the auto-runner stuff. Sure, you can just leave the game running (or even not running, and coins and souls rack up when you’re not playing), but there are missions and requirements where you need to interact. Like, boost so many times, or collect boxes that require you to jump, or enter and complete bonus levels which are tricky (the first few times, but not when you’ve done them over 200 times) platforming timed-jump challenges with big money rewards. If you don’t do these hands-on bits, you progress much, much less quickly. And, since this game is months long (yes, I’ve been playing it for months, off and on) you have to take part or it’ll be years.
In terms of completing it, I bought everything. All upgrades, all items, all unlocks. There’s no “congraturation you sucsess” and there’s no credit roll, but I literally ran out of things to do, so as far as I’m concerned, I’m done. Should you play it? No. It might be free but it’s stupid and too time consuming and there are a few bits in your progress where it takes too long between improvements. Like, when you first hit Billions of coins, it takes hours to accumulate them and reach the next milestone. Same when you get to Octillions. But you skip over Trillions so fast you barely notice they exist. There’s a bit of a pacing issue, and I can’t help feel it’s intentional to get you to cave and spend Real Actual Money to skip these slow bits. I think I’d have prefered to pay a bit for the game and not have to deal with Crawl or Pay.
